JP5656352B2 - Multilayer piezoelectric actuator - Google Patents

Description

  The present invention relates to a laminated piezoelectric actuator that converts electrical input energy into mechanical energy such as displacement and force. More specifically, the invention relates to a laminated piezoelectric actuator that can be used for a long period of time without causing deterioration of characteristics even under severe operating environments. It relates to an actuator.

  A conventional multilayer piezoelectric actuator has a structure in which an external electrode is bonded to a side surface of a multilayer body in which a plurality of piezoelectric layers made of a piezoelectric material and conductive internal electrode layers are alternately stacked with a conductive adhesive. Yes. When such a laminated piezoelectric actuator is used for a long time in a severe use environment such as a high temperature atmosphere, various problems such as a problem that a stress is applied to the conductive adhesive and a crack occurs. This is because when the actuator is driven, that is, when the laminated body expands and contracts in the laminating direction due to piezoelectric displacement, stress is applied to the conductive adhesive disposed on the side surface of the laminated body. This is because cracks occur in the conductive adhesive. When a crack occurs, the internal electrode layer and the external electrode cannot ensure electrical continuity through the conductive adhesive, resulting in inconvenience such as poor conduction.

As a means for improving the conduction failure, for example, in the technique described in Patent Document 1 below, the external electrode provided on the side surface of the piezoelectric laminate is connected to the internal electrode, and the metal layer A laminated piezoelectric actuator composed of a conductive elastic body formed thereon is disclosed. This is to disperse / relax the stress applied to the external electrode by the conductive elastic body when the laminate is expanded and contracted, thereby preventing the occurrence of cracks.
JP 2001-313428 A

  However, in the background art as described above, the connection to the internal electrode is performed by a base metal layer formed by a method such as plating, and a conductive elastic body that relieves stress is formed on the base metal layer. ing. The base metal layer is a portion to which a stress is applied directly when the laminate is stretched. Further, since the base metal layer is less stretchable than the conductive elastic body, it may not be able to sufficiently follow the deformation of the laminate. Therefore, there is a problem that the stress applied to the external electrode cannot be sufficiently relaxed and cracks cannot be sufficiently prevented.

  The present invention focuses on the above points, and its purpose is to provide a multilayer piezoelectric actuator having an external electrode structure that does not cause deterioration of characteristics due to cracks or the like even when used for a long time in a harsh environment. Is to provide.

In order to achieve the above object, the present invention includes a substantially columnar piezoelectric body, a lead embedded in the piezoelectric body, and exposed at an end surface of the piezoelectric body. In a laminated piezoelectric actuator having a plurality of internal electrodes sandwiched between, and an external electrode formed on an end face where the lead portion of the piezoelectric element body is exposed and electrically connected to the internal electrode, The external electrode is divided in the stacking direction of the internal electrodes, and includes a plurality of base metals connected to the lead portions of the internal electrodes, and a conductive elastic layer connecting the plurality of base metal layers. The conductive elastic layer is made of conductive silicone rubber, and each of the plurality of base metal layers has one base metal layer connected to a lead portion of two or more internal electrodes, and the piezoelectric body Between the element body and the elastic layer A plurality of base metal layers are formed separately, and the conductive elastic body layer is formed of conductive silicone rubber, so that it is between adjacent base metal layers, and the piezoelectric body and the elastic body. A gap is formed between the body layer and the body layer .

  The above and other objects, features and advantages of the present invention will become apparent from the following detailed description and the accompanying drawings.

According to the present invention, a plurality of internal electrodes stacked in a piezoelectric body and external electrodes connected at the end faces of the base body are divided in the stacking direction of the internal electrodes and connected to a lead portion of the internal electrodes. A base metal layer and a conductive elastic layer connecting the plurality of base metal layers are formed. In this case, conductive silicone rubber is used as the conductive elastic layer, and each of the plurality of base metal layers is connected to one base metal layer with two or more internal electrode lead portions , and the piezoelectric body The plurality of base metal layers are divided and formed between an element body and the elastic body layer, and the conductive elastic body layer is formed of conductive silicone rubber so that the adjacent base metal layers are formed. Te, and, between the piezoelectric element and the elastic body layer, it was Rukoto form a gap. This relieves stress on the underlying metal layer, absorbs stress by the elastic layer, and follows the element displacement well. There is an effect that a laminated piezoelectric actuator that does not cause deterioration can be obtained.

  Hereinafter, the best mode for carrying out the present invention will be described in detail based on examples.

  First, Embodiment 1 of the present invention will be described with reference to FIGS. 1A is a side view of the multilayer piezoelectric actuator of the present embodiment, FIG. 1B is a front view of (A) seen from the direction of the arrow FA, and FIG. 2 is a front view of the multilayer body of the present embodiment. FIG. As shown in FIGS. 1 and 2, in the multilayer piezoelectric actuator 10 of this embodiment, a plurality of internal electrodes 16 and 18 are alternately formed in a piezoelectric body (piezoelectric body) 14 with a piezoelectric body interposed therebetween. In addition, external electrodes 20 and 26 are provided on the end face of the laminated body 12. The piezoelectric body 14 has a substantially columnar shape, and the lead portion 16A of the internal electrode 16 is exposed on one end surface of the piezoelectric body 14, and the lead portion 18A of the internal electrode 18 is exposed to the piezoelectric body. The other end surface of the element body 14 is exposed.

  In such a laminated piezoelectric actuator 10, it is known that stress due to expansion and contraction of the laminated body 12 is applied to the external electrode. Therefore, in the present invention, even when the laminated piezoelectric actuator 10 is used for a long time under a severe environment, the external electrodes 20 and 26 have a two-layer structure so as not to cause deterioration of characteristics due to cracks or the like. More specifically, the external electrode 20 is divided in the stacking direction, and has a plurality of base metal layers 22 connected to the lead portions 16 </ b> A of the internal electrodes 16, and conductivity that connects the plurality of base metal layers 22. The elastic body layer 24 is used. Similarly, the external electrode 26 is divided in the laminating direction, and a plurality of base metal layers 28 connected to the lead portions 18A of the internal electrode 18 and a conductive elastic layer connecting the plurality of base metal layers 28. 30.

  In the illustrated example, two lead portions 16 A are connected to one base metal layer 22, and two lead portions 18 A are connected to one base metal layer 28. The two adjacent base metal layers 22 are arranged with an interval x (see FIG. 2), and the two adjacent base metal layers 28 are arranged with an interval x. The elastic layers 24 and 30 are provided at substantially central portions of the base metal layers 22 and 28, and are set to have a width such that the base metal layers 22 and 28 are exposed from both sides.

  Such an external electrode structure exhibits the following operational effects. By dividing the base metal layers 22 and 28 into a plurality of layers in the stacking direction, the stress applied to each of the base metal layers 22 and 28 can be reduced. In addition, although the portion of the interval x expands and contracts, the stress due to the expansion and contraction of the portion of the interval x does not apply to the base metal layers 22 and 28, so that the stress can be reduced accordingly. Then, by connecting the divided base metal layers 22 and 28 by the elastic layers 24 and 30, the stress applied to the external electrodes 20 and 26 is absorbed and reduced, and the elastic layers 24 and 30 are stacked. It follows the displacement of the body 12 well. Therefore, it is possible to prevent the external electrodes 20 and 26 from cracking due to long-term use in a harsh environment and to prevent deterioration such as migration. For example, when it is expanded and contracted 1 billion times under the condition of AC 200 V-50 Hz and 150 ° C., the displacement amount is reduced to 80% in the conventional multilayer piezoelectric actuator, whereas in the multilayer piezoelectric actuator of the present invention, There was no decrease in displacement.

  Here, the distance x (see FIG. 2) between the base metal layers 22 and 28 is formed to be smaller than twice the thickness of the piezoelectric body sandwiched between the internal electrode 16 and the internal electrode 18. The internal electrode lead portions 16A and 18A exposed at the respective end faces are exposed with an interval twice as large as the thickness of the piezoelectric body, so that the interval x is smaller than twice the thickness of the piezoelectric body. The stress applied to the underlying metal layers 22 and 28 can be relaxed, and the connection with the internal electrodes 16 and 18 can be sufficiently ensured.

  As a material for forming the piezoelectric body 14, either a lead or a non-lead material may be used. Further, as the internal electrodes 16 and 18, for example, Pt, Ag, Pd, Pd, Cu, Ni or the like is used. The base metal layers 22 and 28 of the external electrode are formed by, for example, screen printing or non-contact coating using a conductive resin paste, Ag, Pd, Cu, Ni paste or the like, and baking or curing. The elastic layers 24 and 30 are formed by bonding to the base metal layers 22 and 28 using, for example, conductive silicone rubber. In consideration of the adhesive strength, the base metal layers 22 and 28 are preferably formed together with the elastic layers 24 and 30 by curing.

  As described above, according to the first embodiment, the plurality of internal electrodes 16, 18 connected to the lead portions 16 A, 18 A exposed at the end face of the piezoelectric body 14 and divided in the stacking direction of the internal electrodes 16, 18. The external electrodes 20 and 26 are composed of the underlying metal layers 22 and 28 and the conductive elastic layers 24 and 30 connecting the plurality of underlying metal layers 22 and 28. Therefore, the base metal layers 22 and 28 and the elastic layers 24 and 30 absorb stress in two stages, and the elastic layers 24 and 30 are excellent in displacement of the laminate 12 or expansion and contraction of the laminate piezoelectric actuator 10. Therefore, even if it is used for a long period of time in a harsh environment, it is possible to prevent the external electrodes 20 and 26 from being cracked, and there is an effect that the characteristics are not deteriorated.

In addition, this invention is not limited to the Example mentioned above, A various change can be added in the range which does not deviate from the summary of this invention. For example, the following are also included.
(1) The shapes and dimensions shown in the above embodiments are merely examples, and may be appropriately changed as necessary. The same applies to the material.
(2) In the above embodiment, the two lead portions 16A and 18A are connected to one base metal layer 22 and 28. However, this is also an example, and three or more lead portions are connected. You may do it.

(3) The elastic layers 24 and 30 shown in the above embodiment are also examples, and as shown in FIG. 3 (A), both end sides of the base metal layer 22 are alternately formed by a plurality of elastic layers 24A. You may make it connect. Alternatively, as in the example shown in FIG. 3B, only one end side of the base metal layer 22 may be connected by the elastic layer 24B. In the illustrated example, the elastic layer 24B is provided on the left end side. However, the elastic layer 24B may be provided on the right side as indicated by a dotted line in the drawing, or may be provided on both end sides. With the configuration shown in FIG. 3B, even if a crack occurs in the elastic layer 24B, the lower portion is a piezoelectric inactive portion, so that a more stable driving state can be maintained. In this case, even if the elastic body layer 24 </ b> B is made of the same material as that of the base metal layer 22, the same effect can be expected.
(4) In order to improve adhesion between the base metal layers 22 and 28 and the elastic body layers 24 and 30, the base metal layers 22 and 28 may be plated. The elastic layers 24 and 30 may also be plated to improve solder wettability.

According to the present invention, the plurality of internal electrodes stacked in the piezoelectric body and the external electrodes connected at the end faces of the base body are divided in the stacking direction of the internal electrodes and connected to the lead-out portions of the internal electrodes. It comprises a plurality of base metal layers and a conductive elastic layer connecting the plurality of base metal layers. In this case, conductive silicone rubber is used as the conductive elastic layer, and each of the plurality of base metal layers is connected to one base metal layer with two or more internal electrode lead portions , and the piezoelectric body The plurality of base metal layers are divided and formed between an element body and the elastic body layer, and the conductive elastic body layer is formed of conductive silicone rubber so that the adjacent base metal layers are formed. Te, and, between the piezoelectric element and the elastic body layer, it was Rukoto form a gap. As a result, the stress applied to the external electrode can be reduced, and the external electrode can follow the element displacement and prevent the occurrence of cracks.

It is a figure which shows the laminated piezoelectric actuator of Example 1 of this invention, (A) is a side view, (B) is the front view which looked at the said (A) from the arrow FA direction. It is a front view of the laminated body of the said Example 1. FIG. It is a front view which shows the other Example of this invention.

Explanation of symbols

10: laminated piezoelectric actuator 12: laminated body 14: piezoelectric body (piezoelectric body)
16, 18: Internal electrodes 16A, 18A: Lead portions 20, 26: External electrodes 22, 28: Underlying metal layers 24, 24A, 24B, 30: Elastic layer

Claims (1)

A substantially columnar piezoelectric element body, and a plurality of internal electrodes embedded in the piezoelectric element body and having a lead portion exposed on an end face of the piezoelectric element body, and stacked with the piezoelectric element in between In the laminated piezoelectric actuator having an external electrode formed on the exposed end face of the piezoelectric element body and electrically connected to the internal electrode,
The external electrode is
Divided in the stacking direction of the internal electrodes, a plurality of base metal layers connected to the lead portion of the internal electrode, and a conductive elastic layer connecting the plurality of base metal layers,
Composed by
The conductive elastic layer is a conductive silicone rubber,
Each of the plurality of base metal layers is connected to one base metal layer with two or more internal electrode lead portions ,
The plurality of base metal layers are divided and formed between the piezoelectric body and the elastic layer, and the conductive elastic layer is formed of conductive silicone rubber, so that the adjacent base metal layer And a gap is formed between the piezoelectric element body and the elastic body layer .

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